Abstracts

Rationale: Seizures can directly lead to brain injury by affecting the structure and function of dendrites, which may contribute to cognitive deficits and progressive epileptogenesis in epilepsy patients. Our previous work using time-lapse multiphoton imaging in vivo showed that kainate-induced status epilepticus causes acute dendritic beading and spines loss in mice [1]. Whether brief seizures also induce dendritic injury is not clear. Here, we investigated the acute effects of seizures of varying durations on dendritic structure of neocortical neurons in vivo. Methods: In vivo multiphoton imaging was used to monitor dendritic changes in mice after different durations of kainate-induced seizures. Adult transgenic mice expressing green fluorescent protein (GFP) in neocortical neurons were used. Animal surgeries were performed as previously reported [1]. Briefly, a cranial window sealed by a cover slip was created over neocortex and screw electrodes were placed adjacent to the cranial window to record EEG. After pre-seizure images were obtained, seizures were induced in mice by i.p. injection of 20 mg/kg kainate. After various cumulative durations of electrographic seizures (5-10 min, 10-20 min, 20-30 min, and 30-40 min), seizures were terminated by isoflurane anesthesia induction for subsequent post-seizure imaging at 0 hr, 1 hr, 2 hr, and 4 hr. Control mice received saline injection instead of kainate. Post-hoc image analysis was performed to evaluate changes in the number of dendritic spines and the beading of dendrites. The beading was categorized as no beading, mild beading, or severe beading, based on previous criteria [1]. Results: Control mice showed no significant change in dendritic spine number and no signs of beading over a 4 hour period. Kainate-induced seizures of all durations induced some acute loss of spines, but the degree of spine loss was directly correlated with the duration of seizures. Seizures with a cumulative duration between 5-10 minutes caused ~25% spine loss, whereas seizures lasting 30-40 minutes caused ~75% spine loss, with intermediate seizure durations having correspondingly intermediary spine loss. In parallel, dendritic beading occurred to varying degrees following kainate-induced seizures and was also directly correlated with the cumulative seizure duration. 5-10 minute seizures caused only mild dendritic beading in less than half of dendrites and no severe beading, whereas 30-40 minute seizures caused severe beading in 100% of dendrites. During the 4 hour post-seizure observation period, there was minimal evidence of recovery of dendritic spines and beading. Conclusions: The severity of seizure-induced dendritic injury worsens with longer seizure durations, but even brief (5-10 minute) kainate seizures may cause some acute dendritic spine loss and mild beading. While the long-term evolution and functional consequences of this seizure-induced dendritic injury need to be investigated further, the present findings raise concerns about the potential damaging effects of relatively brief seizures. Supported by NINDS and CURE. 1. Zeng et al. J Neurosci 2007;27:11604-13.